1. Field of the Invention
The present invention relates to the art of resetting a printed-wiring-board supporting device which supports a printed wiring board (PWB), and particularly relates to the art of shortening a time needed to reset the PWB supporting device. A PWB with electric components (e.g., electronic components) being mounted thereon should be called as a printed circuit board (PCB) but, in the present specification, a PCB is also referred to as a PWB, for avoiding complexity.
2. Discussion of Related Art
Generally, a PWB includes a thin substrate formed of an electrically insulating material such as a synthetic resin, and a circuit pattern formed of an electrically conductive material on the thin substrate. Thus, the PWB has flexibility. Therefore, when electric components (ECs) are mounted on the PWB, or when an adhesive or a creamed solder is applied to the PWB for mounting of ECs, the PWB cannot maintain an accurate flatness, unless a back surface of the PWB is supported at a considerably large number of points.
To solve this problem, Japanese Patent Document No. 7-15189 teaches applying a negative pressure or suction to a PWB and thereby holding the same. More specifically described, the document discloses a PWB holding device including a base plate and a plurality of holding pins. The base plate has a plurality of negative-pressure-supply holes each of which opens in an upper surface thereof and is connected via a negative-pressure passage formed therein to a negative-pressure-supply source. Each of the holding pins includes an elongate pin portion and a container-like seat portion, and the pin portion has a passage which is formed therethrough in an axial direction thereof and is communicated with an inner space of the seat portion. Each holding pin is attached to the upper surface of the base plate, such that a lower-end surface of the seat portion thereof is held in close contact with a portion of the upper surface that surrounds the opening of one negative-pressure-supply hole. In this state, the inner passage of the pin portion is communicated with the negative-pressure-supply hole via the inner space of the seat portion, so that negative pressure is supplied to the inner passage and is applied to a lower or back surface of a PWB to support the same. Thus, the PWB holding device is a PWB supporting device which has the function of sucking and holding a PWB.
The holding pins support the back surface of the PWB that is opposite to the front surface for which an operation, such as mounting of ECs, is performed. However, the holding pins must not engage uneven portions of the back surface of the PWB itself or the ECs mounted on the back surface. Therefore, the holding pins must be engaged with only limited portions of the back surface of the PWB and, depending upon those limited portions of the back surface, the holding pins must be attached to only limited portions of the upper surface of the base plate. Thus, the holding pins are attached to selected ones of the negative-pressure-supply holes of the base plate, and the remaining supply holes to which the holding pins are not attached are closed with respective caps to avoid the leakage of negative pressure.
However, conventionally it is an operator who sets the holding pins on the base plate and attaches the caps to the negative-pressure-supply holes free of the holding pins, and accordingly it takes a long time to reset the PWB holding device. When a current sort of PWBs are changed to a new sort of PWBs for each of which an operation is to be performed, the PWB holding device is reset by moving the holding pins from the current positions to new positions to support the new sort of PWBs. However, this resetting operation needs a long time.
This problem occurs to not only a PWB supporting device which includes holding pins each for applying negative pressure to a PWB and thereby holding the same but also a PWB supporting device which does not have the function of applying negative pressure to a back surface of a PWB and thereby holding the same but includes closing-pins each for supporting, at a support surface thereof, a back surface of a PWB and thereby supporting the same. The latter PWB supporting device does not require the operator to attach caps to negative-pressure-supply holes, but it needs a long time for the operator to set the closing-pins at respective prescribed positions. Thus, it takes a long time to reset the latter PWB supporting device as well.